The art of compounding various additives into masses of thermoplastic resin in order to modify the properties of products manufactured from the resin is a major aspect of plastics technology. Although each segment of the plastics additives industry has its unique problems, the addition of pigment to color plastics is probably the most important and the most difficult.
The problems in color compounding begin with the fact that, while there is an unlimited number of color variations which can be created in plastics, precise color matching is often necessary. Small variations in color within an individual plastic part or among the parts of a plastic product can easily be detected even by an untrained eye and are not acceptable, particularly in consumer products. The color which will be rendered by a given combination of pigments can vary a great deal depending on the nature of the base resin, variations in the pigments themselves, and the quality of the dispersion of the pigments in the base resin. The fact that most pigments do not easily disperse in masses of resin and that improper dispersion of the pigment can cause deterioration of the properties of the plastic such as specking or streaking and can add to the difficulties of coloring.
Various approaches have been developed to solve the problem of color matching and consistency. In one approach, the plastics processor or molder mixes the natural polymer (which he has purchased from a resin manufacturer) with suitable quantities of powdered pigments and provides his own quality control. Because of the high state of technology relating to the matching and mixing of the pigments to achieve proper color and dispersion with the plastic mass, and because of the health and the aesthetic problems resulting from the airborne dust generated by dry pigments, this approach is not practical for the great majority of molders, Furthermore, contamination and housekeeping is a definite problem where colored dust is present.
In a second approach, the resin manufacturer provides the resin to the molder in a mixed and precolored final form. In general, the extremely large firms which are in the business of manufacturing the natural resin, find it impractical to supply the specific color and additive combinations desired by the molders, except for a few very common formulations.
The result is a third approach, the development of the custom compounding industry whose function is to modify the standard compounds manufactured by the resin producers into products which are suited to the specific needs of individual molders. This approach has the problem that it still requires the manufacture of large quantities of specially-formulated plastic which has to be stored in sufficient quantities to avoid shortages and, therefore, is subject to destruction and obsolescence. The precolored or compounding approach is also substantially more costly because it involves another step in preparing usable plastic resin, entirely by-passed when adding a concentrate. The compounding step also adds to the heat history of a plastic resin, thus reducing its ability to withstand degradation during processing in the final step of fabricating a useful part. The storage of quantities of various colors of compounded plastic resin also consumes considerable space and ties up costly capital unnecessarily.
Most recently the custom compounding industry has offered to the molder an additive concentrate which the molder can mix into this natural resin using simple and inexpensive techniques. The additive concentrates are specifically formulated, so that, when they are mixed in proper proportion into the natural resin, the final mixture has the specific properties desired by the molder. The concentrates are provided in a form which is easy to handle, easy to disperse in the base resin, and does not have the dusting and other undesirable properties of normal additives.
Several types of additive concentrates are in use. In one form, the additive is dispersed in a carrier of the same plastic to which the concentrate is to be added or one of easier flow or a compatible plastic. In this way, compatibility problems between the carrier and the natural resin are avoided. However, because most plastics will only accept a relatively low concentration of additive before they are capable of absorbing no more, a large volume of the concentrate of relatively low additive concentration must be used in the final mixture. Also, a given concentrate with its specific carrier resin is normally only compatible in a single type of base resin, thus, limiting the usefulness of a given concentrate formulation.
Another type of concentrate called "liquid color," involves a suspension of additive in a liquid carrier. While a fairly high concentration of additive can be provided, additive distribution in the final product is not always satisfactory and, because the vehicle is often not compatible with the base resin, the physical properties of the base resin may sometimes be adversely effected. The liquid vehicle often causes the color to streak and for this reason does not perform quite as well as concentrate. A further type of concentrate involves dispersions of the additive in a wax base. While very high concentrations can be achieved, the wax base very often adversely effects the properties of the plastic mixture and the processing conditions. These and other difficulties experienced with the prior art systems have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide an additive concentrate particle which can be added to a mass of thermoplastic resin in a simple manner.
Another object of this invention is the provision of an additive concentrate particle which will provide a uniform and consistent distribution of the additive within the let-down or dilution resin.
A further object of the present invention is the provision of an additive concentrate particle which is completely non-dusting in transportation and use.
It is another object of the instant invention to provide an additive concentrate particle which is capable of carrying an extremely high concentration of the additive, so that the amount of concentrate which must be added to the dilution resin is minimized.
A still further object of the invention is the provision of an additive concentrate particle which has good physical properties, can, therefore, be handled and used with simple and convenient techniques, and can be used with existing dispensers.
It is a further object of the invention to provide an additive concentrate particle having a carrier which improves many physical properties of the final resin mix.
It is a still further object of the present invention to provide an additive concentrate particle whish is compatible with a wide range of dilution resins.
With the foregoing and other objects in view, which will appear as the description proceeds, the invention resides in the combination and arrangement of steps and the details of the composition hereinafter described and claimed, it being understood that changes in the precise embodiment of the invention herein disclosed may be made within the scope of what is claimed without departing from the spirit of the invention.